The present invention relates to a memory device and, more particularly, to a memory device with a standby function which is connected to a microcomputer.
A conventional memory device connected to a microcomputer has a built-in chip enable terminal (hereinafter simply referred to as "CE" terminal) which sets the memory device to a standby state in order to prevent wasteful power consumption when a memory included in the memory device is not selected. In a conventional microcomputer applied system, an address outputted from the microcomputer is decoded by means of an external circuit. If the address outputted does not specify an address of the memory included in the memory device, the CE terminal is set inactive so that the memory device is set to a standby state. Recently, however, in order to dissolve a bus bottleneck in a microcomputer applied system, there has been developed and been in practical use a process in which a special protocol is introduced between the microcomputer and the memory device, and a read address for the memory is not outputted each time from the microcomputer but only instruction codes flow through a bus sequentially. Since this process has a built-in address pointer which holds the address on the side of the memory device and is incremental in response to a synchronous signal from the microcomputer, it is not necessary to output the address each time from the microcomputer. Therefore, it is possible to supply the microcomputer with instruction codes efficiently. It is, however, impossible to decode the address by means of the external circuit mentioned above to set the memory device to a standby state.
As explained above, the conventional process which does not output the read address from the microcomputer to an external unit in order to overcome a bus bottleneck has a problem in that, even if the microcomputer itself assumes a standby state of a low power consumption, total power consumption of the microcomputer applied system as a whole does not decrease due to a lack of a process which sets the memory device to a standby state. Therefore, a power supply circuit of the microcomputer applied system and a backup circuit against a power breakdown become large-scale, which results in an increase in the cost of manufacturing the system.